Microstructure Of Solder Joints Research Articles

Microstructure, IMCs layer and shear property of Sn-9Zn solder joints reinforced by Cu nanoparticles during thermal cycling

Microstructure, IMCs layer and shear property of Sn-9Zn solder joints reinforced by Cu nanoparticles during thermal cycling

Effect of adding Ni nanoparticles on the melting characteristics, mechanical properties and intermetallic compound growth of Sn58Bi solder

Purpose This paper aims to investigate the improvement of Sn58Bi solder properties by Ni nanoparticle to provide theoretical support in the field of electronic packaging. Design/methodology/approach In this study, nickel nanoparticles (Ni NPs) were doped into Sn58Bi solder as a reinforcing agent to prepare a composite solder. The wettability of composite solder, melting characteristics of solder alloy, microstructure of joints, mechanical properties and intermetallics growth at the interface were investigated. Findings Test results show that Ni had little substantial effect on the solders alloy melting temperature yet decreased the alloy undercooling. Notably, Ni enhanced solders wettability on Cu substrates. The spreading area increased by 14% at 0.6 wt.% Ni. The Ni refined the microstructure of Sn58Bi solder joints and inhibited the coarsening of the Bi-rich phase in the solder. At the same time, it also led to the production of free intermetallic compounds, increasing growth of the intermetallic compound (IMC) layer. However, upon surpassing 0.6 wt.% Ni, (Cu, Ni)6Sn5 accumulated and formed irregular clumps in the matrix. The grain size of the IMC layer gradually decreased as Ni was added. In shear tests, the fracture of joints occurred mainly inside the solder matrix. Sn58Bi-0.6Ni joints displayed a 40% rise in shear strength and a 25% rise in Vickers hardness. In addition, the appearance of dimples at the fracture indicated the improved flexibility of joints. Originality/value In this paper, Ni nanoparticle with different contents were added to Sn58Bi solder to prepare a composite solder, and the properties of the composite solder were investigated from different perspectives.

SnAgCu Solder Joint Microstructure Evolution During Thermal Aging: Influence of Flux

An intermetallic layer (IML) between the solder alloy and the soldered surface affects the mechanical and electrical performance of the resulting joints. Numerous studies have explored the possibilities of influencing the IML to achieve more reliable interconnections. However, the type and composition of the used flux, crucial for the proper creation of solder joints, is rarely included as a possible influencing factor. In this article, a comprehensive study on the interfacial microstructure evolution of lead‐free SnAgCu solder joints, accounting for the flux type and the temperature of the preheating phase of reflow soldering, where the flux contained in the solder paste becomes active, is presented. In the results, it is shown that the IML of as‐reflowed and thermally aged solder joints depends significantly on the flux. The IML activation energy is 57% higher for rosin‐based low‐activity (ROL)0 flux compared to ROL1 flux. The ROL0 flux, containing fewer active components, also outperforms the ROL1 flux in both the mechanical and electrical properties of the joints. Furthermore, the temperature profiles also show slight differences in measured properties, with the fluxes responding differently to changes in preheating temperature. In the presented results, importance of the used flux on solder joint microstructure is demonstrated.

Dendrite Growth in Single-Grain and Cyclic-Twinned Sn–3Ag–0.5Cu Solder Joints

The microstructure of electronic solder joints is generated by the solidification of a small volume of bulk undercooled liquid. Here, we study β-Sn dendrite growth in Sn–3Ag–0.5Cu in the specific geometry and nucleation conditions of ball grid array (BGA) solder joints by combining electron backscatter diffraction and imaging of microstructures. It is shown that, while ⟨110⟩\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\langle 110\\rangle$$\\end{document} is the preferred dendrite growth direction, out-of-plane branching and growth with ⟨11W⟩\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\langle 11W\\rangle$$\\end{document} directions are important for allowing dendrites to fan out into the spheroidal volume of BGA joints due to the low symmetry of β-Sn. We find that the crystallographic orientation of β-Sn at the nucleation point plays a strong role in subsequent dendrite growth. In single-grain joints, dendrites are often unfavorably oriented for growth, resulting in different types of zig-zag dendrite growth. In cyclic-twinned joints, it is shown how competitive out-of-plane trunk growth between three dendrite orientations produces {101} boundaries and the characteristic beachball microstructure.

Effects of soldering temperatures and composition on the microstructures and shear properties of Sn58Bi-xSAC0307/ENIG solder joints

PurposeThis paper aims to systematically study the effects of reflow temperature and SAC0307 (SAC) content on the micromorphology and mechanical properties of Sn58Bi-xSAC0307 composite solder joints to meet the requirements of high integration and low-temperature packaging of devices and provide references for the application of composite solder joints.Design/methodology/approachSn58Bi and SAC0307 solder paste was mechanically mixed in different proportions to prepare Sn58Bi-xSAC0307/ENIG solder joints. The thermal properties, microstructure and mechanical properties of the composite solder joints were studied.FindingsAs SAC content in the solder increases, the balling temperature of SnBi-SAC solder gradually increases. The addition of SAC alloy reduces the grain size of large Bi-rich phase, and there are small-sized dispersed Bi and Ag3Sn particles in the bulk solder. The intermetallic compounds composition of the SnBi-xSAC/ENIG solder joint changes from Ni3Sn4 to (Ni, Cu)3Sn4 and (Cu, Ni)6Sn5 with SAC increasing. As the soldering temperature increases, the strength of all solder joints shows a rising trend. Among them, the shear strength of SnBi-20SAC solder joints at a reflow temperature of 150°C is approximately 37 MPa. As the reflow temperature increases to 250°C, the shear strength of solder joints increases to approximately 67 MPa.Originality/valueThis study provides a reference for the optimization of low-temperature solder composition and soldering process under different package designs.

The role of microstructure in the thermal fatigue of solder joints

Thermal fatigue is a common failure mode in electronic solder joints, yet the role of microstructure is incompletely understood. Here, we quantify the evolution of microstructure and damage in Sn-3Ag-0.5Cu joints throughout a ball grid array (BGA) package using EBSD mapping of localised subgrains, recrystallisation and heavily coarsened Ag3Sn. We then interpret the results with a multi-scale modelling approach that links from a continuum model at the package/board scale through to a crystal plasticity finite element model at the microstructure scale. We measure and explain the dependence of damage evolution on (i) the β-Sn crystal orientation(s) in single and multigrain joints, and (ii) the coefficient of thermal expansion (CTE) mismatch between tin grains in cyclic twinned multigrain joints. We further explore the relative importance of the solder microstructure versus the joint location in the array. The results provide a basis for designing optimum solder joint microstructures for thermal fatigue resistance.

The preparation and wettability of the Sn-9Zn-2.5Bi-1.5In solder paste for SMT process and high shear ball performance

Purpose This study aims to focus on the surface mount technology (SMT) mass production process of Sn-9Zn-2.5Bi-1.5In solder. It explores it with some components that will provide theoretical support for the industrial SMT application of Sn-Zn solder. Design/methodology/approach This study evaluates the properties of solder pastes and selects a more appropriate reflow parameter by comparing the microstructure of solder joints with different reflow soldering profile parameters. The aim is to provide an economical and reliable process for SMT production in the industry. Findings Solder paste wettability and solder ball testing in a nitrogen environment with an oxygen content of 3,000 ppm meet the requirements of industrial production. The printing performance of the solder paste is good and can achieve a printing rate of 100–160 mm/s. When soldering with a traditional stepped reflow soldering profile, air bubbles are generated on the surface of the solder joint, and there are many voids and defects in the solder joint. A linear reflow soldering profile reduces the residence time below the melting point of the solder paste (approximately 110 s). This reduces the time the zinc is oxidized, reducing solder joint defects. The joint strength of tin-zinc joints soldered with the optimized reflow parameters is close to that of Sn-58Bi and SAC305, with high joint strength. Originality/value This study attempts to industrialize the application of Sn-Zn solder and solves the problem that Sn-Zn solder paste is prone to be oxidized in the application and obtains the SMT process parameters suitable for Sn-9Zn-2.5Bi-1.5In solder.

Comparing the Solderability of Different SA C0307 Composite Solder Pastes

In the present study, the effect of four oxide ceramics (TiO2, ZnO, ZrO2, and CuO) as reinforcements were investigated on the soldering parameters of the SAC 0307 solder alloy. The oxide ceramics were used in nano-powder format. Composite solder pastes were composed by the standard ball milling process of the nano-particles into the SAC 0307 solder paste in 0.25wt% weight fraction. The wettability, shear strength, and microstructure of the composite solder joints were studied and compared. The ceramic nano-particles did not have a major effect on the wettability of the solder. Shear strength increases were observed at the composite joints, except in the case of ZnO. Generally, Sn grain refinement was found in the Sn-matrix which could be the reason for the shear strength increase.

Influence of doping Si3N4 nanoparticles on the properties and microstructure of Sn58Bi solder for connecting Cu substrate

Purpose This study aims to explore the feasibility of adding Si3N4 nanoparticles to Sn58Bi and provides a theoretical basis for designing and applying new lead-free solder materials for the electronic packaging industry. Design/methodology/approach In this paper, Sn58Bi-xSi3N4 (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0 Wt.%) was prepared for bonding Cu substrate, and the changes in thermal properties, wettability, microstructure, interfacial intermetallic compound and mechanical properties of the composite solder were systematically studied. Findings The experiment results demonstrate that including Si3N4 nanoparticles does not significantly impact the melting point of Sn58Bi solder, and the undercooling degree of solder only fluctuates slightly. The molten solder spreading area reached a maximum of 96.17 mm2, raised by 19.41% relative to those without Si3N4, and the wetting angle was the smallest at 0.6 Wt.% of Si3N4, with a minimum value of 8.35°. When the Si3N4 nanoparticles reach 0.6 Wt.%, the solder joint microstructure is significantly refined. Appropriately adding Si3N4 nanoparticles will slightly increase the solder alloy hardness. When the concentration of Si3N4 reaches 0.6 Wt.%, the joints shear strength reached 45.30 MPa, representing a 49.85% increase compared to those without additives. A thorough examination indicates that legitimately incorporating Si3N4 nanoparticles into Sn58Bi solder can enhance its synthetical performance, and 0.6 Wt.% is the best addition amount in our test setting. Originality/value In this paper, Si3N4 nanoparticles were incorporated into Sn58Bi solder, and the effects of different contents of Si3N4 nanoparticles on Sn58Bi solder were investigated from various aspects.

Changes in the Microstructure and Electrical Resistance of SnBi-Based Solder Joints during Current Stressing

Changes in the Microstructure and Electrical Resistance of SnBi-Based Solder Joints during Current Stressing

Transient liquid phase bonding of Sn-Pb solder with added Cu particles

In this paper, the 1%-20% Cu particles were uniformly distributed in SnPb solder by mechanical mixing method to prepare composite solder. The solder was welded by eutectic welding and the high temperature failure test was carried out. The melting point and internal structure of solder were observed before reflow, after welding and after aging, and the existence of high-temperature resistant skeleton was found. It could be seen from the DSC curve that the solder absorption peak changes in a step-like manner, and the proportion of the high melting point absorption peak gradually increases with the aging process. The micro-structure of solder joints showed that a thin layer of IMC was formed around the Cu particles in the solder joints after welding, and the IMC in the solder joints had grown continuously until they contacted each other and formed a skeleton structure with aging. The skeleton structure improved the high temperature resistance of the solder joint. EDS analysis showed that the distribution of Cu element in the solder was similar to that of Sn, and the Pb element was enriched. The distribution of metal elements indicates that the solder joint was mainly composed of Cu6Sn5 IMC skeleton and Pb rich phase, and the solder component phase was high melting point component transformation.

Addressing Challenges in Dual Sided SiP Thermal Budget

System-in-Package (SiP) has been adopted as the mainstream advanced packaging technology in many consumer applications including 5G smartphones, tablets, wireless earbuds, smart wearables, etc. Heterogeneous integration, smaller form factor, better electrical performance, lower cost of assembly and faster time to market are the key differentiators of SiP as compared to conventional packaging techniques. In applications such as 5G mobile RF Front-End (RFFE) and Antenna-in-package (AiP) modules, dual sided SiP is the popular approach which brings even higher level of integration and smaller form factor. However thermal warpage control is a significant challenge during two times of solder reflow processes for the front and back sides of the package, especially if one side is with underfill and mold materials which have significant CTE mismatch to the substrate and dies, causing delamination failures and yield losses. This study examines the novel solution of reducing thermal budget with the use of a low temperature solder paste material based on SnBiAg alloy in ultra-fine pitch Type 6 solder powders. It allows a minimal peak reflow temperature of only 170 °C that effectively reduces warpage of dual sided SiP substrates. Solder alloy and paste properties and solder joint microstructures are examined in detail for tests including fine-pitch printing and component soldering, thermal aging test on different substrate finishes, thermal cycling test and mechanical drop test for reliability performance.

Growth of intermetallic compounds and their reinforcement on CrCoNi/Au80Sn20 soldering interfaces

To broaden the utility of the CrCoNi medium entropy alloy in engineering applications, it is imperative to conduct a comprehensive investigation into its soldering capabilities. This study is centered on a detailed examination of the microstructure and mechanical properties of solder joints formed between Au80Sn20 and CrCoNi through vacuum soldering. Nonetheless, the interaction between the solder and the alloy leads to the formation of an intermetallic compound layer with a specific thickness. Raising the soldering temperature results in an expanded contact area and an increase in the shear strength of the joints. This can be attributed to the enhanced diffusion and atom migration at elevated temperatures.Moreover, the hardness of the intermediate layer exceeds that of both the medium entropy alloy and the Au80Sn20 alloy. This is primarily due to the strengthening effects brought about by the presence of Ni and Co in the alloy. This study underscores the importance of thoroughly investigating soldering techniques for the medium entropy alloy. It also provides valuable insights into the mechanical characteristics and microstructure of the resulting solder joints.

Influence of Isothermal Aging on Microstructure and Shear Property of Novel Epoxy Composite SAC305 Solder Joints.

With the rapid iteration of microsystem integrated technology, the miniaturization of electronic devices requires packaging materials with higher reliability. In this work, the microstructure evolution and mechanical properties of novel epoxy composite SAC305 solder joints were studied after isothermal aging to evaluate the enhanced effect of epoxy addition. The thickness variation and morphological evolution of the interfacial layer were analyzed. The results showed that, as the aging time was prolonged, the Cu6Sn5 interfacial layer remarkably coarsened and Cu3Sn compounds formed between the Cu6Sn5 layer and Cu pad due to the continuous atomic diffusion. Compared with the monolithic joint, the epoxy composite SAC305 joints had a lower overall IMC growth rate during aging, closely related to the initial morphologies of the interfacial layers. The shear test results showed an apparent decrease in the shear forces of all the solder joints as the aging time increased. Nevertheless, because of the extra mechanical support provided by the epoxy layer, the epoxy composite joints demonstrated notably enhanced mechanical properties. After 1000 h aging treatment, the shear force of SAC305 joints containing 8 wt.% epoxy was 26.28 N, showing a 24.08% increase over the monolithic joint. Cu-Sn IMCs were detected on the shear fracture of the monolithic joint after 1000 h aging, indicating the fracture occurred near the interface and displayed a ductile/brittle mixed fracture. Concerning the epoxy composite joints, cracks were still initiated and extended within the solder bulk, demonstrating a noticeable enhancement in ductility due to the addition of epoxy.

Effect of Microwave Hybrid Heating on Mechanical Properties and Microstructure of Sn3.0Ag0.5Cu/Cu Solder Joints

Microwave hybrid heating (MHH) has become soldering’s alternative method for lead-free solder alloys due to its benefits towards modern microtechnology, such as shorter processing time, lower energy consumption and lower defect rate. Nonetheless, it still requires susceptors to improve its heating performance, such as SiC, which is known for its high loss factor under low microwave frequencies. In this study, the effect of microwave hybrid heating on mechanical properties, as well as the microstructure of solder joint between Sn3.0Ag0.5Cu (SAC305) solder alloy and Cu substrate was investigated. Solder joint was created using MHH with different soldering parameters (amount of SiC in a range of 3-7g and exposure time in a range of 7-10min) between SAC305 solder alloy (in the form of wire and paste) and Cu substrate. Then, a lap shear test was carried out following a standard of ASTM D1002 to determine solder joint strength. Characterization was made using an optical microscope and scanning electron microscopy. Results showed that solder wire produced the highest solder joint strength with the value of 115.45 MPa when using 3.05g of SiC for 8.92min soldering time. Meanwhile, the solder paste produced 109.76MPa solder joint strength when using 3.03 g of SiC for 9.39 min soldering time. The intermetallic compound (IMC) form was scallop-like Cu6Sn5, both solder/substrate joints with a thickness of 2.87 μm for solder wire and 3.62 μm for solder paste. Nonetheless, an excessive amount of SiC would generate more heat in MHH and increase the IMC thickness as well as reduce shear strength, which eventually decreases the solder joint stability.

Fatigue performance and microstructure of lead-free solder joints in BGA assembly at room temperature

One of the crucial factors in evaluating the reliability of an electronic appliance is fatigue failure of the interconnecting solder joints. In most situations, large bulk samples are used to investigate the fatigue characteristics of the solder materials. Only a few studies have examined the solder joints frequently observed in ball grid array (BGA) components. This study implemented a specialized test vehicle in BGA assembly connecting two substrates with nine identical solder joints. Four SAC-based solder alloys were tested using an Instron micromechanical tester in the stress-controlled and strain-controlled methods at room temperature and constant strain rate. At two distinctive stress and strain levels, the fatigue performance of alloys featuring organic solderability preservative (OSP) and electroless nickel-immersion gold (ENIG) surface finishes was investigated. The fatigue results obtained from the stress-controlled and strain-controlled tests were compared. Microstructural analysis was performed using scanning Electron Microscopy (SEM) and energy dispersive spectroscopy (EDS) to identify the precipitates in the bulk solder and the morphologies of IMC layers. The thickness of intermetallic compound (IMC) layers and the failure mode were examined in each case. The results demonstrated that the OSP surface finish significantly outperformed the ENIG surface finish regardless of the testing process and solder alloy. Various failure modes were observed, depending on the solder alloy and IMC layer.

Effect of Trace Boron Nitride Nanoparticles on the Microstructure and Shear Properties of Sn58Bi Solder Joint

Effect of Trace Boron Nitride Nanoparticles on the Microstructure and Shear Properties of Sn58Bi Solder Joint

Microstructure and mechanical properties of Sn-xGa alloys and solder joints

Though Ga is a promising addition used in third-generation lead-free solders for harsh-environment applications, its influences on βSn structure and mechanical properties of solder alloys/joints are still unknown. This study demonstrated that Ga additions in Sn-XGa (X = 0.5, 1.0, 2.0 in wt%) can moderately refine βSn grains but render the alloys more susceptible to recrystallization during cross-section and polishing. Sn-1.0Ga shows substantially elevated yield/tensile strengths (45.1 MPa/64.9 MPa) compared with pure Sn, attributed to the strong solid-solution strengthening effect of Ga, and it also possesses good tensile ductility of >25%. Compared with pure Sn and Sn-3.0Ag-0.5Cu (SAC305) solder joints on Cu, Sn-XGa/Cu solder joints show significantly reduced dissolution of Cu substrate that benefits in suppressing the formation of primary Cu6Sn5. Among Sn-XGa/Cu, Sn-2.0Ga/Cu joint exhibits high shear strength (69.4 MPa) comparable to that of SAC305/Cu joint (70.5 MPa), owing to the Ga solid-solution strengthening and the extra second-phase strengthening from Cu9Ga4.

Microstructure and shear properties evolution of Mn-doped SAC solder joint under isothermal aging

Microstructure and shear properties evolution of Mn-doped SAC solder joint under isothermal aging

A Fast Method to Estimate Through-Bump Current for Power Delivery Verification

Due to the mismatch between the package scaling and the relentless silicon technology scaling, the limited power supply bumps have to bear more stresses on bump reliability. A too high through-bump current may induce increased thermal and mechanical issues, thereby damaging the integrity of solder joint micro-structure. Thus, it is critical to analyze the through-bump current under different test scenarios at sign off to ensure bump integrity. Since the full chip power delivery verification needs to solve a linear system with billions of nodes, it is then very time-and resource-consuming to repeatedly conduct such bump integrity check during ECO. In this paper, we present a fast through-bump current estimation methodology for power delivery verification, which can significantly reduce the computational complexity while maintaining accuracy. Experimental results demonstrate that the proposed methodology can achieve very high accuracy with a relative error of around 0.6% and a maximum error of around 1.5% across 4 different designs with 1-2 orders of magnitude speed-up.